This invention concerns a process for the manufacture of sections of thermoplastic resin reinforced with continuous fibers and the equipment for producing such a product. The process comprises coating rovings that have the fibers that constitute them arranged in the form of a sheet prior to passing into the coating zone, then, in order to ensure impregnation of the fibers of the rovings, passing the aggregate into a forced impregnation zone prior to passing to the channel for shaping the final product. The coating zone is fed in a known manner by at least one extruder.
It is known, for example, from U.S. Pat. No. 3,834,980 to coat rovings with thermoplastic resin. According to the known methods of coating, the rovings are passed through the central heated body of a coating head, the coating being effected by means of a supply of molten thermoplastic resin from the known system.
A roving comprises the combination of several continuous elementary fibers.
In the known methods of coating for the manufacture of thermoplastic sections reinforced with continuous fibers, several rovings are generally combined in the form of a bobbin. In this method, there are two major problems that have not been solved. The first consists in the difficulty of thoroughly impregnating the bobbins and homogenously distributing the thermoplastic resin around each one of the elementary fibers. The second, which is a consequence of the first, is to eliminate from the finished product, air trapped between the fibers which impairs the mechanical properties of the finished product.
In U.S. Pat. No. 3,993,726, it is possible to impregnate a roving separately by placing in the impregnation zone, two series of baffles arranged substantially perpendicular in relation to each other. In this manner, the roving is expanded and impregnated in one direction and then flattened in an opposite direction in the second series of baffles. This device has a two-fold disadvantage. First, the arrangement is useful for the impregnation of a single roving; due to the arrangement of the baffles, it is not possible to impregnate individual fibers of rovings in sheet form since a sheet cannot undergo a rotation of about 90.degree. in a channel full of plastic material without the fibers gathering in a mass. The second inconvenience results from the arrangement of the baffles in the equipment; all the baffles are arranged in the channel which causes a double flattening of the roving directly in the molten plastic material and, therefore, requires considerable tension force on the fibers at the exit of the channel which results in breakage of the fibers. Under these conditions, the quality of impregnation of the fibers is not good; the flexural characteristics obtained in the finished product are low. The effectiveness of the reinforcement characterized by the .epsilon. coefficient is low, and generally does not exceed 0.25.
U.S. Pat. No. 4,312,917 describes a process for coating individual rovings in a channel filled with molten plastic material. The process has the disadvantages of the process of U.S. Pat. No. 3,993,726, and adds another problem. in that the rovings brought from the outside are introduced in the coating channel substantially perpendicular to the axis of the channel which creates additional rupturing stresses and an entanglement of the fibers starting from the second baffle because the cold rovings carry a solidified layer of the impregnating resin on their surface.